1. Field of the Invention
The present invention relates to a white smoke generating apparatus which generates white smoke by means of placing water in contact with a cryogenic gas such as liquid nitrogen, liquid air or liquid carbon dioxide gas, and then vaporizing this gas.
2. Background Art
In the prior art, white smoke generating apparatuses for use in enhancing the stage effects of various shows and events, such as that shown in FIG. 7, are known.
This type of white smoke generating apparatus generates white smoke by blasting a cryogenic gas such as liquid nitrogen, liquid air or liquid carbon dioxide gas onto the surface of water, stored in a storage tank, and then vaporizing this gas: the water spray accompanying the aforementioned condenses thereby generating white smoke.
In the following, an example is described in which liquid nitrogen (hereafter referred to as LN.sub.2) is employed as the cryogenic gas.
White smoke generating apparatus 1 shown in FIG. 7, generates white smoke 56 by spraying LN.sub.2 onto the surface 60 of warm water 58, and then vaporizing this LN.sub.2. This white smoke generating apparatus 1 mainly comprises a fixed or mobile water tank 2 for storing warm water 58; an LN.sub.2 spray opening 3 comprising a spray structure such as a spray nozzle or the like for spraying LN.sub.2 onto water surface 60 of water tank 2; a discharge opening 4, provided above water surface 60 of water tank 2, for discharging into the air white smoke 56, generated when LN.sub.2 comes in contact with warm water; and a heater 5 for heating and maintaining the temperature of the warm water 58.
A side surface 2a of this water tank 2 is equipped with a liquid level indicator 6 and a water supply pipeline, while the bottom face 2b is equipped with a water pipeline 8 for use in drainage.
In addition, mist trap 9 is a filter installed in discharge opening 4 for removing the mist contained in the white smoke 56. LN.sub.2 is stored inside a thermally insulated pressure vessel 10 for use in low temperature storage.
In order to generate white smoke 56 using this white smoke generating apparatus 1, water is poured into water tank 2 up to a predetermined depth, and this water is then heated to a predetermined temperature (usually to approximately 30.degree.-80.degree. C.) using heater 5. The valve of thermally insulated pressure vessel 10 is then opened, and LN.sub.2 is supplied to LN.sub.2 spray opening 3 and sprayed onto the surface 60 of the warm water 58, thereby coming into contact with the warm water. In this manner, white smoke 56 is generated, and after the mist in the white smoke 56 is removed by mist trap 9, this generated white smoke 56 is discharged into the air via discharge opening 4.
Stoppage of the generation of white smoke 56 is performed by closing the valve of thermally insulated pressure vessel 10 which interrupts the supply of LN.sub.2 to LN.sub.2 spray opening 3.
However, prior art white smoke generating apparatus 1 is disadvantageous in that the usage amount of the cryogenic gas (e.g. LN.sub.2) is approximately the same as the yield of white smoke 56, thus the running cost of the LN.sub.2 is significantly large. In particular, in the case when it is necessary to generate a large amount of white smoke 56 to enhance the stage effects of various shows and events, a considerably large amount of LN.sub.2 must be consumed, resulting in significant cost increases.
In addition, other disadvantages exist in that when continuously generating the white smoke 56 over long periods of time, although the warm water 58 is heated to maintain its temperature, due to the extremely low temperature of the LN.sub.2 (approximately 77.degree. K.), the water surface 60 freezes which in turn reduces the vaporization efficiency of LN.sub.2, consequently lowering the yield of the white smoke.
The present invention takes into consideration the aforementioned, and provides a white smoke generating apparatus which is able to prevent freezing of the water surface and also to prevent subsequent reduction of the white smoke yield, and which also effectively reduces the usage amount of the cryogenic gas.